Get everything down on paper with the agreed date and what not. Not done by then, pull out and get it done by a more reputable place. Those excuses are probably b/c he needs more time to figure out what he is doing. If and when it does finally get done, might turn out to be a hacked up job.
I was in the same predicament for my NA to TT swap and ended up with my Z being down for almost a year and then having to take it to another shop to solve the existing issues once I got it back.